1. Field of Invention
This invention relates generally to thermotherapy applicators adapted to direct a stream of hot air toward a localized skin surface of a patient overlying a problem region; the air stream exhibiting a pulsatory heat wave pattern which promotes the transfer of heat to the problem region, and more particularly to an improved control unit for such applicators.
2. Status of Prior Art
Medical practitioners since ancient times have known that the application of heat to the body is useful in the relief of muscle soreness and various aches and pains, as well as in the treatment of certain pathological conditions. Thus the use of heat for the treatment of arthritis and other abnormalities is now commonplace. Hot water bottles and electrical heating pads are in widespread use, not merely to provide warmth, but also to afford a degree of relief or therapy for various conditions. In applying heat to the surface of the body, one may do so by convection, by direct contact with a body to be warmed; that is, by conduction, or by radiating energy into the body.
Difficulty has heretofore been experienced in effectively applying heat which is electrically or otherwise generated to a patient. When transferring heat inwardly through living tissue to a problem region underlying the skin, if the heat applied to the skin surface is within a tolerable temperature range, then not enough heat energy is transferred to this site to afford beneficial effects.
In conventional heat applicators, the heat is applied continuously to the skin area overlying the problem region. This imposes strict limits on the acceptable temperature level. Thus if one seeks to have the heat penetrate more deeply into the body, the temperature at the surface area must be raised to promote more rapid heat transfer, for the higher the differential between the internal and external temperatures, the greater the rate of transfer. But a point is then quickly reached at which the patient is made uncomfortable, for one can only tolerate continuously applied heat when its temperature level is not excessively above body temperature.
The temperature sensitivity threshold for a given patient is that temperature level of the heating medium to which the patient is continuously exposed, above which the patient experiences serious discomfort.
Because continuous heat therapy techniques, to be completely safe, must operate at a relatively low temperature level not much higher than the sensitivity threshold, they are of limited effectiveness in the treatment of backache and other painful conditions that are relieved by heat.
The Guibert U.S. Pat. No. 4,667,658 discloses a technique for applying therapeutic heat to a localized skin surface overlying a problem region. In this technique, the skin surface is exposed to a heating medium whose temperature is at a base level that is well above ambient but no higher than the temperature sensitivity threshold, the temperature of the medium being periodically raised above base level to create high heat energy pulses whose peak temperatures are much higher than the threshold.
The duty cycle of these pulses is such as to allow for internal heat transfer to take place in the problem region below the exposed area of the patient in the intervals between pulses to an extent preventing an excessive rise in temperature at the skin surface whereby the patient gains the benefit of high heat energy treatment without discomfort or injury.
To carry out this technique, the Guibert '658 patent discloses a system in which a motor-driven centrifugal air blower operated at a constant speed draws air from the atmosphere at ambient temperature and blows this air through an applicator which can be oriented to direct the hot air stream to impinge on the localized skin surface of the patient being treated, the hot air then being discharged into the atmosphere.
Mounted at the inlet of the blower motor is an electrical heater coil which acts to heat the air drawn into the blower. An electronic controller is interposed between the heater element and a high voltage supply to energize the heater with a relatively low voltage to establish the base temperature level in the pulsatory heating pattern to which the patient is subjected. The electronic controller is periodically bypassed by means of a repeat cycle timer, whereby the high voltage from the supply is then directly applied to the heater element to raise the air temperature well above the base level to create high energy pulses whose peaks are much higher than the threshold.
The difficulty with the Guibert '658 arrangement in which the voltage applied to the heater is modulated, is that because of thermal inertia, clearly defined heat peak pulses are not produced.
The Guibert et al. U.S. Pat. No. 5,190,031 discloses a thermotherapy applicator in which a fan driven by a d-c motor blows air through an a-c powered heater coil to produce a stream of hot air that is directed toward a localized skin surface, the air stream exhibiting a pulsatory heat wave pattern in which the temperature cyclically alternates from a base to a peak level.
In the Guibert et al. '031 applicator, the temperature to which the air is raised depends on the velocity of air blown by the fan through the heater coil, the greater the air velocity, the lower the temperature level. An electronic control system is associated with the fan motor to periodically change the fan velocity from a predetermined high value at which the resultant temperature level of the air stream is at a base level above ambient but no higher than sensitivity threshold of the patient being treated, to a predetermined low velocity value at which the resultant temperature level is raised above the base level to create high temperature heat pulses whose peaks are well above the sensitivity threshold.
To produce periodic changes in air velocity, the d-c motor driving the fan is energized by a d-c power supply connected to a 120 VAC power line, the supply including a step-down transformer whose output is rectified to field a low voltage d-c output corresponding to the rated voltage of the motor (12 VDC).
Connected in series between the output of the rectifier and the input to the motor is a resistor which drops the voltage applied to the d-c motor to a level somewhat below its rated value. This resistor is periodically short-circuited by a repeat cycle timer so that in each timed cycle of operation, the voltage applied to the motor input alternates from its rated value (12 VDC) to a reduced value (8 VDC), thereby causing the air velocity to alternate cyclically from a high velocity to a low velocity.
It is important to understand the relationship between the velocity of air passing through the heater and the amount of heat imparted to this air by the heater. When the fan is operating at high speed, as a consequence of which the air passes quickly through the heater coil, then the amount of heat imparted to the air in the course of its transit through the coil will be small, resulting in a relatively low rise in air stream temperature. When, however, the fan is operating at low speed and the air then passes slowly through the heater coil, then more heat will be imparted to the air in the course of its transit through the heater coil. This will result in a relatively high rise in air stream temperature.
In the Guibert et al '031 applicator, when the motor operates at its rated voltage, the fan velocity is then high and the air is heated to a base level above ambient temperature but somewhat below the sensitivity threshold of the patient. When the motor operates at below its rated voltage and the fan velocity is low, the air is then heated to an elevated peak temperature level well above the sensitivity threshold.
The difficulty experienced with the applicator arrangement disclosed in the Guibert et al. '031 patent is that it is relatively inflexible and cannot be readily accommodated to the needs of a particular patient. No two patients have the same temperature sensitivity threshold, and a peak temperature level set for one patient may be too high or too low for another.